[PATCH] D109553: [SCEV] Attempt to define what flags are legal on a SCEV

[Philip Reames via Phabricator via llvm-commits]

reames added inline comments.


================
Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:13512
               getMulExpr(getUDivExpr(URemLHS, URemRHS), URemRHS,
-                         (SCEV::NoWrapFlags)(SCEV::FlagNUW | SCEV::FlagNSW));
           RewriteMap[V] = Multiple;
----------------
efriedma wrote:
> I think the expression here is naturally nuw: `(X /u Y) * Y` must be less than or equal to X.  No idea why it's getting marked nsw, though.
> 
> Anyway, we can deal with various violations (e.g. ScalarEvolution::getGEPExpr) in future patches.
I agree on the definitional nature of the nuw.  I'll simplify point out that because it is definitional, it should be in getMulExpr, not here.  Interestingly, it's not.  

I'd still argue for removing here since it appears to have no test coverage.

I hadn't noticed the issue in getGEPExpr previously, that one is nasty.   I'm going to go ahead and file a bug to keep track of the issues as we find them.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D109553/new/

https://reviews.llvm.org/D109553